There are notable differences between Irish neutrality and traditional types of neutral states:

While most[citation needed] neutral states maintain strong defence forces, Ireland has a relatively small defence force of approximately 10,500 personnel[3]

While most[citation needed] neutral states do not allow any foreign military within their territory, Ireland has a long history of allowing military aircraft of various nations to refuel at Shannon Airport. Under the Air Navigation (Foreign Military Aircraft) Order, 1952,[4] the Minister for Foreign Affairs, exceptionally, could grant permission to foreign military aircraft to overfly or land in the State. Confirmation was required that the aircraft in question be unarmed, carry no arms, ammunition or explosives and that the flights in question would not form part of military exercises or operations.

A neutral state may also allow its citizens to serve in the armed forces of other, possibly belligerent, nations. Ireland does not restrict its citizens from serving in foreign armies and significant numbers of Irish citizens serve or have served in the British and to a lesser extent United States armies and the French Foreign Legion.[citation needed]

The Spanish Civil War (Non-Intervention) Act, 1937 made it an offence to travel from Ireland to Spain to fight for either side in the Spanish Civil War.[21] This applied both to Irish citizens and nationals of many other European countries.[22] Nevertheless, there was Irish involvement in the Spanish Civil War on both sides by private individuals and groups.

De Valera stated in his wartime speeches that small states should stay out of the conflicts of big powers; hence Ireland's policy was officially "neutral", and the country did not publicly declare its support for either side although in practice, while Luftwaffe pilots who crash-landed in Ireland and German sailors were interned, Royal Air Force (RAF), Royal Canadian Air Force (RCAF), and United States Army Air Forces (USAAF) pilots who crashed were usually allowed to cross the border into British territory (although some Allied personnel were also interned[26]). The internees were referred to as "guests of the nation". The German embassy had to pay for their keep. If they were on a non-combative mission they were repatriated. While it was easy for Allied pilots to make that claim, it was not realistic for Luftwaffe pilots to make a similar claim. Towards the end of the war, the German embassy was unable to pay, so the internees had to work on local farms. Strict wartime press censorship had the effect of controlling a moral reaction to the war's unfolding events and reiterated the public position that Irish neutrality was morally superior to the stance of any of the combatants.[27]

Allied aircraft were allowed to overfly County Donegal to bases in County Fermanagh. Many of these aircraft were manufactured in the United States, to be flown by the RAF. This was known as the Donegal Corridor. Navigational markings are still, faintly, visible on mountains, such as Slieve League. There were many unfortunate crashes into these mountains. The bodies of dead airmen were handed over at the border. At the border the Guard of Honour performed a drill with reversed arms, a Bugler sounded the Last Post and a Chaplain gave a Blessing. An Allied officer, embarrassed that the coffins' journeys were being continued in open lorries, thanked the Irish for the "honour". The reply was: "Ours is the honour, but yours is the glory".[28]

USAAF aircraft en route to North Africa refuelled at Shannon Airport, flying boats at nearby Foynes. A total of 1,400 aircraft and 15,000 passengers passed through Foynes airport during the war years.

In the course of the war an estimated 70,000 citizens of neutral Ireland served as volunteers in the British Armed Forces (and another estimated 50,000 from Northern Ireland,[27] and this figure does not include Irish people who were resident in Britain before the war (though many used aliases). Those who had deserted the Irish Army to serve in the British Army, on returning to Ireland were stripped of all pay and pension rights, and banned for seven years from any employment paid for by state or government funds.[29] Some 200,000 Irish migrated to England to participate in the war economy— most of them stayed after the war. Those who went without proper papers were liable to be conscripted. Irish military intelligence (G2) shared information with the British military and even held secret meetings to decide what to do if Germany invaded Ireland to attack Britain, plans which were formulated into Plan W, a plan for joint Irish and British military action should the Germans invade. However the Commander of the Irish Second Division based on the Northern Ireland border General Hugo McNeill had private discussions with the German Ambassador Edouard Hempel about German military assistance in the event of a British invasion from the north.[30] De Valera declined Germany's offer of captured British weapons.[31] The Germans did have a plan to simulate an invasion Ireland called Operation Green similar to the Allies Operation Bodyguard but it was only to be put into operation with the plans to conquer Britain, Operation Sea Lion.

Irish weather reports were crucial to the timing of the D-Day landings.[32]

On Easter Tuesday, 15 April 1941, 180 Luftwaffe bombers attacked Belfast. De Valera responded immediately to a request for assistance from Basil Brooke, Prime Minister of Northern Ireland. Within two hours, 13 fire tenders from Dublin, Drogheda, Dundalk and Dún Laoghaire were on their way to assist their Belfast colleagues. De Valera followed up with his "they are our people" speech and formally protested to Berlin. Joseph Goebbels instructed German radio not to repeat their report of the raid as Adolf Hitler was surprised at the Irish reaction, which might influence Irish Americans to bring the United States into the war. Although there was a later raid on 4 May, it was confined to the docks and shipyards. (See Belfast blitz).

Ireland wanted to maintain a public stance of neutrality and refused to close the German and Japanese embassies. Unlike many other non-combatant countries, Ireland did not declare war on the near-defeated Germany, and therefore did not seize any German assets. Other neutral countries like Sweden and Switzerland expelled German embassy staff at the end of the war, as they no longer represented a state, but the German legation in Dublin was allowed to remain open.

Irish neutrality during the war was threatened from within by the Irish Republican Army (IRA) who sought to provoke a confrontation between Britain and Ireland. This plan collapsed however when IRA chief of staffSeán Russell died in a U-boat off the Irish coast as part of Operation Dove; the Germans also later came to realise they had overestimated the abilities of the IRA. The American Ambassador, David Gray stated that he once asked de Valera, early in the war, what he would do if German paratroopers 'liberated' Derry. According to Gray, de Valera was silent for a time and then replied "I don't know". De Valera viewed the IRA threat to the authority of the state as sufficiently significant to intern 5,000 IRA members without trial at the Curragh Camp for the duration of the war.

Many German spies were sent to Ireland, but all were captured quickly as a result of good intelligence and sometimes the ineptitude of the spies. The chief spy of Abwehr was Hermann Görtz. In 1983 RTÉ made Caught in a Free State, a dramatised television series about Görtz and his fellow spies.

As Ireland was neutral, Irish cargo ships continued to sail with full navigation lights. They had large tricolours and the word "EIRE" painted large on their sides and decks. At that time, Allied ships travelled in convoy for protection from the U-boat 'wolfpacks'. If a ship was torpedoed, it was left behind since the other ships could not stop for fear of becoming a target. Irish ships often stopped, and they rescued more than 500 seamen, and some airmen, from many nations. However many Irish ships were attacked by belligerents on both sides. Over 20% of Irish seamen, on clearly marked neutral vessels, lost their lives, in the Irish Mercantile Marine during World War II.

While civilian aircraft in other countries were frequently requisitioned for military purposes, Aer Lingus continued to fly a service between Dublin and Liverpool throughout the war.[33]

Winston Churchill, the British wartime Prime Minister, made an attack on the Irish Government and in particular Éamon de Valera in his radio broadcast on VE Day. Churchill maintained that the British government displayed restraint on the Irish state while the de Valera government were allowed to "frolic with the Germans". Churchill maintained that the British could have invaded the Irish state but displayed "considerable restraint" in not doing so. De Valera replied to Churchill in a radio broadcast:[34]

Mr. Churchill makes it clear that in certain circumstances he would have violated our neutrality and that he would justify his action by Britain's necessity. It seems strange to me that Mr. Churchill does not see that this, if accepted, would mean that Britain's necessity would become a moral code and that when this necessity became sufficiently great, other people's rights were not to count….this same code is precisely why we have the disastrous succession of wars… shall it be world war number three?

Ireland applied to join the United Nations in 1945, but this was blocked by an objection by the Soviet Union in the security council.[35]Sean MacBride considered that the UN boycott of Ireland was originally agreed at the 1945 Yalta Conference by Churchill and Joseph Stalin.[36] Despite MacBride's belief, the United Kingdom fully supported Ireland's applications to join the UN.[37](Ireland eventually joined the United Nations in 1955.)

During the Cold War, Ireland maintained its policy of neutrality. It did not align itself officially with NATO – or the Warsaw Pact either. It refused to join NATO because Northern Ireland was still a part of the United Kingdom.[38] Ireland offered to set up a separate alliance with the USA but this was refused. This offer was linked in part to the $133 million received from the Marshall Aid Plan.

However, secret transmission of information from the government to the CIA started in 1955. The link was established by Liam Cosgrave via a Mr Cram and the Irish embassy in London, and was not revealed until December 2007.[39] In 1962–63, during the Cuban Missile Crisis, Seán Lemass authorised searches of aircraft that stopped over at Shannon en route between Warsaw Pact countries, and Cuba, for "warlike material".[40]

The majority of the Irish people have always cherished Ireland's military neutrality, and recognise the positive values that inspire it, in peace-time as well as time of war. Neutrality has been the policy of the State in the event of armed conflict and has provided the basis for Ireland's wider efforts to promote international peace and security.

In February 2006, the Minister for DefenceWillie O'Dea announced that the Irish government would open talks on joining the European Union battle groups. O'Dea said that joining the battlegroups would not affect Ireland's traditional policy of military neutrality, and that a UN mandate would be required for all battlegroup operations with Irish participation. Green Party foreign affairs spokesperson John Gormley condemned the decision, saying that the government was "discarding the remnants of Irish neutrality".[42]

Under Enda Kenny, the Fine Gael party has questioned Irish neutrality, with Kenny claiming that "the truth is, Ireland is not neutral. We are merely unaligned."[43]

Despite its policy of neutrality, Ireland has supplied the NATO-led ISAF mission in the 2001–present Afghanistan War with a running total of 120 Irish troops as trainers.[44][45] The troops are provided under United Nations mandate.[44] As at 8 June 2011, there were seven personnel there.[44]